1. Field of the Invention
The present invention relates to a chucking apparatus for holding a recording disk, and to a recording disk drive motor having the chucking apparatus.
2. Background Art
FIG. 10 shows a recording disk drive motor using a conventional chucking apparatus. A rotation member 1 of the motor includes a shaft 3 rotatably supported by a sleeve 2 which is a bearing member, a rotor holder 4 fixed to an upper portion of the shaft 3 in an axial direction of the rotation member 1, and a chucking apparatus 5 fixed to the shaft 3 at its portion higher than the rotor holder 4 in the axial direction. The chucking apparatus 5 includes a centering case 5a which is fitted into a recording disk 6, and a plurality of chuck pawls 5c which are arranged on the centering case 5a at equal distances from one another in a circumferential direction of the centering case 5a. The chuck pawls 5c are biased radially outward by resilient members 5b, respectively. The chucking apparatus 5 also includes a plurality of centering inclined portions 5d for centering the recording disk 6. A recording disk mounting surface 4b for mounting the recording disc 6 is formed on a radially outer end of a bottom surface 4a of the rotor holder 4. A rubber 4c is fixed to an upper side of the recording disk mounting surface 4b. 
To mount the recording disk 6 on the motor, a central through hole of the recording disk 6 is aligned with the plurality of centering inclined portions 5d of the chucking apparatus 5 and in this state, the recording disk 6 is mounted on the centering case 5a. When the central through hole of the recording disk 6 starts fitting around the centering case 5a, the chuck pawls 5c are pushed by an inner peripheral surface of the central through hole of the recording disk 6 and moved radially inward of the recording disk 6. If the recording disk 6 is completely mounted and placed on the rubber 4c, tip ends 5c1 of the chuck pawls 5c are pushed by resilience of the resilient member 5b and the tip ends 5c1 push an upper peripheral edge of the inner peripheral surface of the central through hole of the recording disk 6. With this, the recording disk 6 is held by the rotation member 1. Therefore, when the rotation member 1 rotates, the recording disk 6 does not come out due to centrifugal force or its own weight or is not inclined.
The chuck pawl 5c has an inclined surface 5c2 which pushes the upper peripheral edge of the inner peripheral surface of the center hole of the recording disk 6. The inclined surface 5c2 is formed with one curved portion directed radially outward. It is preferable that a force required for mounting the recording disk is smaller. Thus, the tip end 5c1 of the chuck pawl 5c is set short. For this reason, it is necessary that a curvature of the inclined surface 5c2 of the chuck pawl 5c which pushes the recording disk 6 is small. Therefore, an angle formed between contact surfaces of the inclined surface 5c2 and the recording disk 6 is adversely increased. For this reason, a pushing force of the chuck pawl 5c against the recording disk 6 is greater on the outer side in the recording disk, and is smaller on the lower side in the axial direction. As a result, when the recording disk 6 is to be detached from a state where the recording disk 6 is held by the rotation member 1, a force required for detaching the recording disk 6 from the rotation member 1 (such a force is called detaching force, hereinafter) is adversely reduced. If the detaching force is reduced, when the rotor rotates, there is an adverse possibility that the recording disk 6 comes out from the rotation member 1 due to the centrifugal force or impact from outside.
If an elastic force of the resilient member 5b is increased to increase the detaching force, e.g., if the resilient member 5b is a coil spring and a spring constant is increased, the detaching force itself can be increased but it becomes difficult to move the chuck pawl 5c in radially inward, and a force required for mounting the recording disk 6 on the rotation member 1 (such a force is called mounting force, hereinafter) is increased. Thus, it becomes difficult to easily mount the recording disk 6 on the rotation member 1 and the operability is deteriorated.
If the elastic force of the resilient member 5b is increased, since the force acting radially outward is increased, a force required for pushing the inner peripheral surface of the central through hole of the recording disk 6 is increased. Thus, the central through hole of the recording disk 6 is deformed by the chuck pawl 5c, and there is a possibility that the central through hole of the recording disk 6 is deviated from the centering inclined portions 5d which center the recording disk 6. As a result, the centering precision of the recording disk 6 is deteriorated, and the recording disk 6 may rotate while deflecting radially.